Users don’t think in terms of getting collections. So filtering by certain user group (adult, child) -> different possibilities from the API.
In The Little Prince, Saint-Exupéry makes three attempts at drawing a sheep for the Prince, Prince isn’t happy until he draws a picture of a box that he says has a sheep inside. -> don’t “recreate the wheel” – use standards [= the box] and provide info e.g. the grass for your sheep is over there.
Give real-world examples in your documentation, not list of operations. Swagger’s good.